Can I "Paint" on my Objects?
1: Select cube in edit mode with A and press Smart UV Project (Cycles blender mode).



2: In UV Image Editor press New Image and create your texture (P.S. don't forget save your texture with F3 save as a image).



3: In Node Editor press check box for use nodes (red box) and with Shift+A from texture menu select: Image Texture and your image.



4: Select Texture Paint and start painting.